During the manufacture of products where metal surfaces provide a base, hand drilled holes are often drilled for purposes of providing an opening for screws which will threaded into the hole and secure another element to that metal surface. There is no reason this is not also true of wooden substrates, but this invention is primarily concerned with solving a problem in the aircraft industry where hand drilled holes sometimes not perpendicular to the surface in which they are drilled. There is a certain degree of latitude in the angularity which is functionally adequate, but eyeball observation of a hole will not necessarily tell the operator whether the angle is sufficiently small as to be acceptable under the circumstances.
After having designed the apparatus illustrated in the drawings, a review of the prior art in the Patent Office was conducted and four patents of interest were discovered, U.S. Pat. Nos. 3,389,475, 2,706,338, 3,109,243, 3,392,453. These references which appear to be the most pertinent are all directed to measuring the angularity of holes drilled in bowling balls and while they relate generally to the subject matter under consideration, each of them includes a plurality of moving parts which can go wrong and which serve only to complicate what is in fact a simple procedure.